The Vegetation of North America 



315 



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Fig. 194. Black spruce trees on the cliffs near Yarmouth, Nova Scotia, showing effects of 

 winds from the Bay of Fundy. 



15 inches, they are more or less confined to the stream margins, 

 and in Alaska to the river valleys. On the best soils the white 

 spruce, balsam fir, and paper birch grow in a dense mixture, 

 forming the finest of northern forest types. The jack pine and 

 white pine in some localities occupy sterile soils and form ex- 

 tensive forests. On mountain slopes and along the shores of the 

 Great Lakes and the sea the black spruce is a common forest 

 tree. In the numerous bogs and poorly drained areas the tama- 

 rack and black spruce dominate. On limestone outcrops and in 

 the better-drained swamps the arbor vitag is common. Where 

 the original forest has been cut or burned over, there are ex- 

 tensive areas covered by birch and aspen poplar. These form 

 only temporary forests that are later succeeded by pine and 

 spruce. 



From northern Minnesota to Nova Scotia the southern portion 

 of the evergreen forest is mixed with the trees of the deciduous 

 forest formation, especially on the best soils and at low elevations. 

 There is an extension of the northern evergreen forest, made up 

 of white pine, hemlock, yellow birch, and spruce, on the Appala- 



